In semiconductor devices represented by, for example, highly integrated circuit elements such as DRAM, there has been a great demand for even higher density, higher integration, and higher speed. Accordingly, in the production fields of various electronic devices, requirements for the establishment of fine processing technology of half-micron order, for example, the development of photolithography technology for fine pattern formation, are becoming more and more severe. In photolithography technology, the formation of a fine pattern requires improved resolution. Here, the resolution (R) of a reduced-projection light exposure device is represented by the Rayleigh's equation R=k·λ/NA (where λ is the wavelength of the exposure light, NA is the numerical aperture of the lens, and k is a process factor). By shortening the wavelength λ of the active energy ray (exposure light) used for the formation of a resist pattern, the resolution can be improved.
As photoresists suitable for short wavelengths, chemically amplified photoresists have been proposed. A chemically amplified photoresist is characterized in that when irradiated with exposure light, a protonic acid is generated from a photoacid generator, which is a component contained in the photoresist, and, as a result of a heating treatment after exposure to light, the protonic acid undergoes an acid-catalyzed reaction with a resist compound or the like. Most of the photoresists currently developed are chemically amplified.
As such acids are generated from a photoacid generator upon exposure to light, an alkane sulfonic acid, an alkane sulfonic acid in which some or all of the hydrogen atoms of the alkyl group of the alkane sulfonic acid are fully fluorinated, and the like are used.
A photoacid generator that generates an alkane sulfonic acid generally generates a weak acid. An alkane sulfonic acid has a problem in that the acid strength for the deprotection of a protective group in a resist compound, such as a tertiary ester group, is not sufficient, resulting in reduced sensitivity and degraded lithography performance, such as LWR.
Meanwhile, in the case of a photoacid generator that generates an alkane sulfonic acid in which all the hydrogen atoms of the alkyl group are fully fluorinated, the acid strength is sufficient for the deprotection reaction of a hard-to-deprotect protective group in a resist compound, and many such photoacid generators have been put to practical use. However, there has been a problem in that because the acid strength is too high, an unexpected reaction occurs during elimination reaction of the protective group for converting the dissolution contrast of the resist compound, resulting in the formation of foreign substances after development or at the time of resist stripping, for example.
Accordingly, in Patent Literature 1, it has been reported that the problem of the formation of foreign substances is solved using a known sulfonic acid having moderate acid strength, in which the hydrogen atoms of the alkyl group of an alkane sulfonic acid are partially substituted with a fluorine atom, a nitro group, or the like, which is an electron-withdrawing group. However, in a compound that generates a sulfonic acid having three or more fluorine atoms, foreign substances are formed after development or at the time of resist stripping, and satisfactory results have not yet been obtained.
In Patent Literature 2, it has been reported that when a compound that generates a sulfonic acid, in which an alkyl group and a perfluoroalkyl group are introduced into the α-carbon atoms of methanesulfonic acid, is used, the sulfonic acid has moderate acid strength without forming foreign substances. However, sufficient acid strength has not yet been obtained. In addition, Patent Literature 3 discloses a sulfonic acid having high acid strength, but sufficient characteristics have not yet been obtained regarding the formation of foreign substances.